This project is concerned with inductive functions exerted from the target organ to the innervating motoneurons in the mammal. When muscle activity is chronically reduced either by transection of the spinal cord or by conduction block of the peripheral nerve, the motoneurons innervating the muscle were found to alter their properties. These changes in motoneuron properties could be prevented by daily activation of the muscle. The factor responsible for the maintenance of motoneuron properties was suggested to be the resultant metabolic changes in the muscle rather than its contractile activity. Prolonged inactivity of sensory fibers arising from a muscle was found to result in enhancement of transmission at synapses on motoneurons. This behavior appears to be related to enhancement of central synaptic efficacy during peripheral sensory regeneration following nerve injuries.